what is the central problem of the story?

Buck is a physically impressive dog. He is a half-Saint Bernard and half-Scottish shepherd living a pampered life in California. The central problem in the story is when he gets dog-knapped and put into doggy slavery (pulling sleds) in the far north. The story i resolved when, after many adventures, Buck finds his alpha-dog wild spirit that has finally surfaced. Buck leaves man and joins the wild for good.